Journal of Superconductivity and Novel Magnetism最新文献

This report presents a design for a double-rod core fluxgate sensor. The design features two identical conventional fluxgate sensors with their excitation coils connected in an anti-parallel configuration while the pick-up coils are interconnected in the same orientation. The purpose of the sensor is to detect displacement in general machining machines. The sensor consists of an excitation coil and a pick-up coil wrapped around a core made of the high permeability amorphous alloy Metglas 2714A ribbon, which has low hysteresis and a highly saturated magnetic field. The cores are bar-shaped and precision-cut with double core layers to increase flux density. The sensor’s high sensitivity of 206 mV/mT and low noise of 0.4 nT/sqrtHz@1 Hz were experimentally determined. In distance measurements, the device has a responsivity of 2.18 V/mm with an initial mounting position to the target of 3 mm. The results indicate that the proposed design is suitable for displacement applications.

Polycrystalline powder samples of La_0.67Sr_0.33−xK_xMn_0.95Ni_0.05O₃ (x = 0.1, 0.125, 0.15) (LSKMNO) were prepared using the sol–gel method (S-G) in this study. The influence of K⁺ doping was systematically investigated on the lattice structure, morphology, and magnetic and magnetocaloric effect (MCE) of LSKMNO. Through the X-ray diffraction (XRD) to confirm the rhombohedral structure of LSKMNO. The magnetic results showed that the Curie temperature (T_C) and the maximum magnetic entropy change ((mathit-{mathitDeltatextit{S}}_textit{M}^text{max})) increase with the K⁺ doping for LSKMNO. The T_C and (mathit-{mathitDeltatextit{S}}_textit{M}^text{max}) for LSKMNO (x = 0.15) were 319 K and 3.59 J/(kg·K) when the external magnetic field (H) was 5 T, respectively. Arrott curve and normalized magnetic entropy curve (({mathitDeltamathit S}_textit{M}mathit/{mathitDeltamathit S}_textit{M}^text{max}mathit-theta)) are plotted to prove that LSKMNO undergoes a second order magnetic phase transition at the T_C attachment.

BaFe_12−xNb_xO₁₉ (x = 0.00, 0.04, 0.08, 0.12, 0.16, and 0.20) with a nominal composition for M-type hexagonal barium ferrite was prepared using solid-state sintering methods. The microstructure and magnetic properties of hexaferrite were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), and vibrating-sample magnetometry (VSM). XRD results revealed that the crystal structure of barium ferrite remained intact after Nb doping, maintaining a single barium ferrite phase. FESEM confirmed the hexagonal crystal structure of the sample. Energy-dispersive X-ray spectroscopy showed increased Nb content and decreased Fe content without the formation of other elements. FTIR revealed bands at 598 and 445 cm⁻¹ corresponding to tetrahedral and octahedral clusters, respectively. The VSM test showed that the saturation magnetization (M_s), residual magnetization (M_r), and coercivity (H_c) initially increased and then decreased with increasing Nb doping, reaching maximum values of 92.297 emu/g, 44.256 emu/g, and 3367.53 Oe, respectively, at x = 0.08.

In the current study, the effect of using different cobalt precursors (cobalt acetate, cobalt acetylacetonate, cobalt chloride and cobalt nitrate) during the synthesis of Co-Fe glycolates on morphology and magnetic properties of CoFe₂O₄ nanoparticles has been investigated. The Co-Fe glycolates, synthesized using different cobalt precursors on calcination, lead to CoFe₂O₄ nanoparticles with different morphologies. Different analytical techniques like TGA, FT-IR, DRS, FE-SEM, TEM, SAED, EDX and XPS were used for the characterization of Co-Fe glycolates and CoFe₂O₄ nanoparticles. XRD studies indicate the formation of cubic CoFe₂O₄ nanoparticles. The Co-Fe glycolates synthesized using cobalt acetate, cobalt acetylacetonate, cobalt chloride and cobalt nitrate as cobalt precursors exhibit hexagon, nanosheet, flower and sphere, respectively. After characterization, a thorough study of magnetic properties (M-H and M-T) for the CoFe₂O₄ nanoparticles was carried out. The M-H studies indicate “wasp-waisted behaviour” in CoFe₂O₄ nanoparticles synthesized from cobalt acetylacetonate, cobalt chloride and cobalt nitrate.

In the theoretical framework of the effective mass envelope function approximation, the energy of impurity state is calculated in In_xGa_1-xAs/GaAs core-shell quantum dot using the plane wave expansion method, and the effects of hydrostatic pressure and temperature are considered. The impurity energy increases with the shell thickness and stabilizes when the shell thickness is greater than 0.4a^*; the impurity energy decreases with the inner core radius; the impurity energy is symmetrically distributed in quantum dot. The application of hydrostatic pressure and temperature do not change the symmetric distribution of impurity state energy. As the hydrostatic pressure (temperature) increases, the energy of the impurity state gradually increases (decreases). The hydrostatic pressure and temperature effects are more pronounced in 1 s state than in 2p± state; the hydrostatic pressure and temperature effects are also more pronounced in the center of the quantum dot.

High-flux ferronickel powder cores are widely used in high-frequency transformers and other fields due to their high saturation flux density and low core loss. In this paper, FeNi@Al₂O₃ composites with varying Al₂O₃ contents (0.0–5.0 wt.%) were prepared. Their microstructure, magnetic properties, and power losses were investigated in detail. SEM morphology indicates that Fe₅₀Ni₅₀ magnetic powders are well coated with Al₂O₃. The loss analysis results show that with the increase of Al₂O₃ concentration, the core loss P_cv first decreased and then increased, and the coating of Al₂O₃ significantly reduced the eddy current loss of FeNi@Al₂O₃ composites. When the content of Al₂O₃ (1 MHz and 50 mT) is 4 wt.%, the core loss is reduced by about 75%.

The existence of antiferromagnetism in rare-earth superconductors exhibits varieties of new physical phenomena. Experiments have highlighted the magnetic specific heat anomalies in antiferromagnetic superconductor. Structured around a Ginzburg-Landau theory, this article presents the role of magnetic field on the specific heat near the antiferromagnetic superconductor phase to normal state phase transition in rare-earth superconductors. The magnetic specific heat is calculated both at the antiferromagnetic superconductor phase and normal state. The qualitative agreement between theory and experiment is discussed.

The impact of partial substitution of erbium and transition metal (zirconium/yttrium/niobium) at bismuth and iron site on multiferroism and magnetoelectric coupling of BFO was studied. Three samples Bi_0.95Er_0.05Fe_0.98X_0.02O₃ (where X = Nb/Zr/Y) were prepared by sol–gel method. The structural, morphological, and elemental aspects of the samples were scrutinized. The ferroelectric, magnetic, and magnetoelectric properties of the samples were recorded. The combined effect of erbium and zirconium offered better saturated ferroelectric loop with greater remnant polarization value (0.74 µC/cm²). On including erbium and zirconium inside bismuth ferrite, the magnetization of BFO got improved very much with remanence value (0.095 emu/g). The combination of erbium and zirconium has intensified the magneto electric behavior in the bismuth ferrite. Interestingly, zirconium inclusion inside the BFO system instead of niobium and yttrium has provoked all the multifunctional aspects uniformly.

Granular high-temperature superconductors (HTSs) are characterized by the hysteretic field dependences of magnetoresistance R(H) and critical current I_C(H). These hysteretic effects are described within the concept of an effective field in the intergrain medium. The effective field is a superposition of external magnetic field H and the field induced by the magnetic moments of superconducting grains into intergrain spacings (grain boundaries). The magnetization of superconducting grains is determined by two contributions: Meissner (shielding) currents (MC) and trapped magnetic fluxes (Abrikosov vortices (AV)). To develop the concept of an effective field in the intergrain medium, the magnetotransport properties (R and I_C) have been compared for two cases: (AV) the magnetization of superconducting grains is only determined by the trapped magnetic flux (zero external field) and (MC) HTS grains are in the Meissner state (the external field is weaker than the first critical field of grains). In a set of experiments, the main features of the hysteretic R(H) and M(H) dependences have been illustrated and the external conditions for implementing the AV and MC states have been established. It has been found that the effects of the Abrikosov vortices and intragrain Meissner currents on an effective field in the intergrain medium at the same magnetization values are noticeably different. This is a nontrivial fact that requires a thorough study of the impact of the anisotropy of the superconducting properties of grains on the configuration of the Meissner currents in them, as well as on the orientation of vortices both inside grains and near their surface. We suggest the explanation of observed stronger effect of the Meissner currents on the intergrain medium as compared with the effect of the Abrikosov vortices.